Vehicle steering apparatus and method

1. A vehicle steering apparatus comprising:

a steering gear that steers steerable road wheels of a vehicle;

a steered angle controller that controls a steered angle of the road wheels;

a manual steering unit that is mechanically separated from the steering gear and manually operated for variably controlling a steering angle;

a steering reaction force actuator that produces a steering reaction force to be applied to the manual steering unit;

a steering reaction force controller that outputs a steering reaction force command value to the steering reaction actuator; and

a road surface input torque detector that detects a road surface input torque inputted to the road wheels from a road surface;

wherein the steering reaction force controller includes a low cut-off frequency filter that extracts a low frequency component equal to or lower than a first predetermined frequency from an output of the road surface input torque detector and sets the steering reaction force command value on the basis of a vehicle driving condition and an output of the low cut-off frequency filter.

2. A vehicle steering apparatus according to claim 1 , wherein the steering reaction force controller further includes a high cut-off frequency filter that extracts a frequency component equal to or lower than a second predetermined frequency that is higher than the first predetermined frequency from the output of the road surface input torque detector and sets the steering reaction force command value in accordance with the vehicle driving condition and a difference between an output of the high cut-off frequency filter and the output of the low cut-off frequency filter.

3. A vehicle steering apparatus according to claim 1 , wherein the steering reaction force controller holds the steering angle constantly at a maximum steering angle when the steering angle reaches the maximum steering angle and sets the steering reaction force command value in a way as to increase the steering reaction force in a pulse-like manner.

4. A vehicle steering apparatus according to claim 1 , wherein the steering reaction force actuator comprises a motor having a clutch.

5. A vehicle steering apparatus according to claim 1 , wherein the road surface input torque detector comprises an axial force sensor that detects an axial force inputted to a rack shaft of the steering gear.

6. A vehicle steering apparatus comprising:

a steering gear that steers steerable road wheels of a vehicle;

steered angle control means that controls a steered angle of the road wheels;

manual steering means that is mechanically separated from the steering gear and manually operated for variably controlling a steering angle;

a steering reaction force actuator that produces a steering reaction force to be applied the manual steering unit;

steering reaction force control means that outputs a steering reaction force command value to the steering reaction force actuator; and

road surface input torque detecting means that detects a road surface input torque inputted to the road wheels from a road surface;

wherein the steering reaction force control means includes a low cut-off frequency filter that extracts a low frequency component equal to or lower than a first predetermined frequency from an output of the road surface input torque detector and sets the steering reaction force command value on the basis of a vehicle driving condition and an output of the low cut-off frequency filter.

7. A vehicle steering apparatus comprising:

a steering gear that steers steerable road wheels of a vehicle;

a steered angle controller that controls a steered angle of the road wheels;

a manual steering unit that is mechanically separated from the steering gear and manually operated for variably controlling a steering angle;

a steering reaction force actuator that produces a steering reaction force to be applied to the manual steering unit; and

a steering reaction force controller that outputs a steering reaction force command value to the steering reaction force actuator,

wherein the steered angle controller includes a disturbance estimation device that estimates a disturbance and determines a disturbance estimation value, and the steering reaction force controller sets the steering reaction force command value in accordance with a vehicle driving condition and the disturbance estimation value estimated by the disturbance estimation device; and

wherein the disturbance estimation device includes a robust compensator used in a robust model matching technique for reducing an error in modeling and an influence of disturbance to the minimum.

8. A vehicle steering apparatus comprising:

a steering gear that steers steerable road wheels of a vehicle;

steered angle control means for controlling a steered angle of the road wheels;

manual steering means mechanically separated from the steering gear and manually operation for variably controlling a steering angle;

a steering reaction force actuator that produces a steering reaction force to be applied to the manual steering means; and

steering reaction force control means for outputting a steering reaction force command value to the steering reaction force actuator;

wherein the steered angle control means includes a disturbance estimation device that estimates a disturbance and determines a disturbance estimation value, and the steering reaction force control means sets the steering reaction force command value in accordance with a vehicle driving condition and the disturbance estimation value estimated by the disturbance estimation device; and

wherein the disturbance estimation device includes a robust compensator used in a robust model matching techniciue for reducing an error in modeling and an influence of disturbance to the minimum.

9. A steering method for a vehicle including a steering gear that steers steerable road wheels of a vehicle, a steered angle controller that controls a steered angle of the road wheels, a manual steering unit that is mechanically separated from the steering gear and manually operated for variably controlling a steering angle, a steering reaction force actuator that produces a steering reaction force to be applied to the manual steering unit, and a steering reaction force controller that outputs a steering reaction force command value to the steering reaction force actuator, the steering method comprising:

detecting a road surface input torque inputted to the road wheels from a road surface and producing an output representative thereof;

extracting a frequency component equal to or lower than a first predetermined frequency from the output; and

setting the steering reaction force command value on the basis of a vehicle driving condition and the output from which the low frequency component equal to or lower than the predetermined first frequency is extracted.

10. A steering method according to claim 9 , further comprising extracting a frequency component equal to or lower than a second predetermined frequency that is higher than the first predetermined frequency from the output, wherein the setting further comprises setting the steering reaction force command value in accordance with the vehicle driving condition and a difference between the output from which the frequency component equal to or lower than the first predetermined frequency is extracted and the output from which the frequency component equal to or lower than the second predetermined frequency is extracted.

11. A steering method for a vehicle including a steering gear that steers steerable road wheels of a vehicle, a steered angle controller that controls a steered angle of the road wheels, a manual steering unit that is mechanically separated from the steering gear and manually operated for variably controlling a steering angle, a steering reaction force actuator that produces a steering reaction force to be applied to the manual steering unit, and a steering reaction force controller that outputs a steering reaction force command value to the steering reaction force actuator, the steering method comprising:

estimating a disturbance and determining a disturbance estimation value; and

setting the steering reaction force command value in accordance with a vehicle driving condition and the disturbance estimation value;

wherein the estimating includes using a robust model matching technique for reducing an error in modeling and an influence of disturbance to the minimum.